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Background: Although numerous endophytic bacteria have been isolated and characterized from cadmium (Cd) hyperaccumulators, the contribution and potential application of the core endophytic microbiomes on facilitating phytoremediation were still lack of intensive recognition. Therefore, a 2-year field sampling in different location were firstly conducted to identify the unique core microbiome in Cd hyperaccumulators, among which the representative cultivable bacteria of different genera were then selected to construct synthetic communities (SynComs). Finally, the effects and mechanisms of the optimized SynCom in regulating Cd accumulation in different ecotypes of Sedum alfredii were studied to declare the potential application of the bacterial agents based on core microbiome., Results: Through an innovative network analysis workflow, 97 core bacterial taxa unique to hyperaccumulator Sedum was identified based on a 2-year field 16S rRNA sequencing data. A SynCom comprising 13 selected strains belonging to 6 different genera was then constructed. Under the combined selection pressure of the plant and Cd contamination, Alcaligenes sp. exhibited antagonistic relationships with other genera and plant Cd concentration. Five representative strains of the other five genera were further conducted genome resequencing and developed six SynComs, whose effects on Cd phytoremediation were compared with single strains by hydroponic experiments. The results showed that SynCom-NS comprising four strains (including Leifsonia shinshuensis, Novosphingobium lindaniclasticum, Ochrobactrum anthropi, and Pseudomonas izuensis) had the greatest potential to enhance Cd phytoremediation. After inoculation with SynCom-NS, genes related to Cd transport, antioxidative defense, and phytohormone signaling pathways were significantly upregulated in both ecotypes of S. alfredii, so as to promote plant growth, Cd uptake, and translocation., Conclusion: In this study, we designed an innovative network analysis workflow to identify the core endophytic microbiome in hyperaccumulator. Based on the cultivable core bacteria, an optimized SynCom-NS was constructed and verified to have great potential in enhancing phytoremediation. This work not only provided a framework for identifying core microbiomes associated with specific features but also paved the way for the construction of functional synthetic communities derived from core microbiomes to develop high efficient agricultural agents. Video Abstract., Competing Interests: Declarations Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Competing interests The authors declare no competing interests., (© 2024. The Author(s).)

The selection of appropriate plants and growth strategies is a key factor in improving the efficiency and universal applicability of phytoremediation. Sedum lineare grows rapidly and tolerates multiple adversities. The effects of inoculation of Acinetobacter sp. phosphate solubilizing bacteria P-1 and application of phosphate rock (PR) as additives on the remediation efficiency of As-contaminated soil by S. lineare were investigated. Compared with the control, both the single treatment and the combination of inoculation with strain P-1 and application of PR improved the biomass by 30.7-395.5%, chlorophyll content by 48.1-134.8%, total protein content by 12.5-92.4% and total As accumulation by 45.1-177.5%, and reduced the As-induced oxidative damage. Inoculation with strain P-1 increased the activities of superoxide dismutases and catalases of S. lineare under As stress, decreased the accumulation of reactive oxygen species in plant tissues and promoted the accumulation of As in roots. In contrast, simultaneous application of PR decreased As concentration in S. lineare tissues, attenuated As-induced lipid peroxidation and improved As transport to shoots. In addition, the combined application showed the best performance in improving resistance and biomass, which significantly increased root length by 149.1%, shoot length by 33%, fresh weight by 395.5% and total arsenic accumulation by 159.2%, but decreased the malondialdehyde content by 89.1%. Our results indicate that the combined application of strain P-1 and PR with S. lineare is a promising bioremediation strategy to accelerate phytoremediation of As-contaminated soils., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

Biochar and metal-tolerant bacteria have been widely used in the remediation of heavy metal contaminated soil. However, the synergistic effect of biochar-functional microbes on phytoextraction by hyperaccumulators remains unclear. In this study, the heavy metal-tolerant strain Burkholderia contaminans ZCC was selected and loaded on biochar to produce biochar-resistant bacterial material (BM), and the effects of BM on Cd/Zn phytoextraction by Sedum alfredii Hance and rhizospheric microbial community were explored. The results showed that, BM application significantly enhanced the Cd and Zn accumulation of S. alfredii by 230.13% and 381.27%, respectively. Meanwhile, BM alleviated metal toxicity of S. alfredii by reducing oxidative damage and increasing chlorophyll and antioxidant enzyme activity. High-throughput sequencing revealed that BM significantly improved soil bacterial and fungal diversity, and increased the abundance of genera with plant growth promoting and metal solubilizing functions such as Gemmatimonas, Dyella and Pseudarthrobacter. Co-occurrence network analysis showed that BM significantly increased the complexity of the rhizospheric bacterial and fungal network. Structural equation model analysis revealed that soil chemistry property, enzyme activity and microbial diversity contributed directly or indirectly to Cd and Zn extraction by S. alfredii. Overall, our results suggested that biochar- B. contaminans ZCC was able to enhance the growth and Cd/Zn accumulation by S. alfredii. This study enhanced our understanding on the hyperaccumulator-biochar-functional microbe interactions, and provided a feasible strategy for promoting the phytoextraction efficiency of heavy metal contaminated soils., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Soil Cd and Zn contamination has become a serious environmental problem. This work explored the performance of wood vinegar (WV) in enhancing the phytoextraction of Cd/Zn by hyperaccumulator Sedum alfredii Hance. Rhizosphere chemical properties, enzyme activities and bacterial community were analyzed to determine the mechanisms of metal accumulation in this process. Results demonstrated that, after 120 days growth, different times dilution of WV increased the shoot biomass of S. alfredii by 85.2%-148%. In addition, WV application significantly increased soil available Cd and Zn by lowing soil pH, which facilitated plant uptake. The optimal Cd and Zn phytoextraction occurred from the 100 times diluted WV (D100), which increased the Cd and Zn extraction by 188% and 164%, compared to CK. The 100 and 50 times diluted WV significantly increased soil total and available carbon, nitrogen and phosphorus, and enhancing enzyme activities of urease, acid phosphatase, invertase and protease by 10.1-21.4%, 29.1-42.7%,12.2-38.3% and 26.8-85.7%, respectively, compared to CK. High-throughput sequencing revealed that the D 100 significantly increased the bacterial diversity compared to CK. Soil bacterial compositions at phylum, family and genera level were changed by WV addition. Compared to CK, WV application increased the relative abundances of genus with plant growth promotion and metal mobilization function such as, Bacillus, Gemmatimonas, Streptomyces, Sphingomonas and Polycyclovorans, which was positively correlated to biomass, Cd/Zn concentrations and extractions by S. alfredii. Structural equation modeling analysis showed that, soil chemical properties, enzyme activities and bacterial abundance directly or indirectly contributed to the biomass promotion, Cd, and Zn extraction by S. alfredii. To sum up, WV improved phytoextraction efficiency by enhancing plant growth, Cd and Zn extraction and increasing soil nutrients, enzyme activities, and modifying bacterial community., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Combined bioaugmentation inoculants composed of two or more plant growth-promoting bacteria (PGPB) were more effective than single inoculants for plant growth and cadmium (Cd) removal in contaminated soils. However, the principles of consortia construction still need to be discovered. Here, a pot experiment with Cd natural polluted soil was conducted and PGPB consortia with different ecological niches from hyperaccumulator Sedum alfredii Hance were used to compare their effects and mechanisms on plant growth condition, Cd phytoextraction efficiency, soil enzymatic activities, and rhizospheric bacterial community of Brassica juncea L. The results showed that both rhizospheric and endophytic PGPB consortia inoculants promoted plant growth (6.9%-22.1%), facilitated Cd uptake (230.0%-350.0%) of oilseed rape, increased Cd phytoextraction efficiency (343.0%-441.0%), and enhanced soil Cd removal rates (92.0%-144.0%). PGPB consortia inoculants also enhanced soil microbial carbon by 22.2%-50.5%, activated the activities of soil urease and sucrase by 74.7%-158.4% and 8.4%-61.3%, respectively. Simultaneously, PGPB consortia inoculants increased the relative abundance of Flavobacterium, Rhodanobacter, Kosakonia, Pseudomonas and Paraburkholderia at the genus level, which may be beneficial to plant growth promotion and bacterial phytopathogen biocontrol. Although the four PGPB consortia inoculants promoted oilseed growth, amplified Cd phytoextraction, and changed bacterial community structure in rhizosphere soil, their original ecological niches were not a decisive factor for the efficiency of PGPB consortia. therefore, the results enriched the present knowledge regarding the significant roles of PGPB consortia as bioaugmentation agents and preliminarily explored construction principles of effective bioaugmentation inoculants, which will provide insights into the microbial responses to combined inoculation in the Cd-contaminated soils., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)